The preclinical unit has focused on elucidating the molecular mechanism(s) of various antidepressant and antimanic treatments. Highlights of the last year include: 1. In vitro and ex vitro studies in rat brain have clearly demonstrated that protein kinase C (PKC) is a target for lithium's actions. Using [3H] PDBu as a quantitative autoradiographic radioligand for PKC, we have demonstrated that chronic (but not acute) lithium treatment produces a marked and significant reduction in [3H] PDBu binding in several hippocampal structures, most notably the CA1 region and subiculum. Immunolabeling with monoclonal antibodies has shown that this is largely due to an isozyme-specific reduction in membrane-associated PKC alpha. 2. In vivo microdialysis of cyclic AMP has shown that chronic lithium increases basal cAMP in rat cortex and hippocampus, while markedly attenuating the response to infused phorbol esters. Ex vivo studies have shown that chronic lithium treatment results in similar effects as phorbol ester treatment - a shift in the sensitivity of the guamine nucletide/Gi heterotrimer dissociation curve to the left. 3. Chronic treatment of rats with different classes of antidepressants reduces the levels of G alpha s and G alpha i1-2 in hippocampus (as assessed by ELISA studies), while producing a complex pattern of effects on G alpha s mRNA, G alpha i1-3 mRNA, G alpha o mRNA, and G alpha q mRNA levels, suggesting that the delayed therapeutic efficacy of these drugs may be due to transcriptional regulation of G protein alpha subunits.